Co-sputter deposition of metal-doped chalcogenides

ABSTRACT

The present invention is related to methods and apparatus that allow a chalcogenide glass such as germanium selenide (Ge x Se 1-x ) to be doped with a metal such as silver, copper, or zinc without utilizing an ultraviolet (UV) photodoping step to dope the chalcogenide glass with the metal. The chalcogenide glass doped with the metal can be used to store data in a memory device. Advantageously, the systems and methods co-sputter the metal and the chalcogenide glass and allow for relatively precise and efficient control of a constituent ratio between the doping metal and the chalcogenide glass. Further advantageously, the systems and methods enable the doping of the chalcogenide glass with a relatively high degree of uniformity over the depth of the formed layer of chalcogenide glass and the metal. Also, the systems and methods allow a metal concentration to be varied in a controlled manner along the thin film depth.

RELATED APPLICATION

This application is a divisional of application no. 11/710,517, filedFeb. 26, 2007 now U.S. Pat. No. 7,446,393, which is a divisional ofapplication no. 10/878,060, filed Jun. 29, 2004, now U.S. Pat. No.7,202,104, issued November 25, 2004, which is a divisional ofapplication no. 10/164,429, filed Jun. 6, 2002, now U.S. Pat. No.6,890,780, issued Dec. 11, 2003. This application is related to thedisclosure of U.S. application No. 10/164,429 of Li et al., filed Jun.6, 2002, now U.S. Pat. No. 6,825,135, entitled ELIMINATION OF DENDRITEFORMATION DURING METAL/CHALCOGENIDE GLASS DEPOSITION. The entirety ofeach related application is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to memory technology. Inparticular, the present invention relates to the fabrication ofmetal-doped chalcogenides.

2. Description of the Related Art

Computers and other digital systems use memory to store programs anddata. A common form of memory is random access memory (RAM). Many memorydevices, such as dynamic random access memory (DRAM) devices and staticrandom access memory (SRAM) devices are volatile memories. A volatilememory loses its data when power is removed. In addition, certainvolatile memories such as DRAM devices require periodic refresh cyclesto retain their data even when power is continuously supplied.

In contrast to the potential loss of data encountered in volatile memorydevices, nonvolatile memory devices retain data for long periods of timewhen power is removed. Examples of nonvolatile memory devices includeread only memory (ROM), programmable read only memory (PROM), erasableprogrammable read only memory (EPROM), electrically erasableprogrammable read only memory (EEPROM), and the like.

U.S. Pat. No. 6,084,796 to Kozicki, et al., entitled “Programmablemetallization cell structure and method of making same,” disclosesanother type of nonvolatile memory device known as a programmableconductor memory cell or a programmable metallization cell (PMC). U.S.Pat. No. 6,084,796 is herein incorporated by reference in its entirety.Such memory cells can be integrated into a memory device, which has beenreferred to as a programmable conductor random access memory (PCRAM). Achalcogenide glass element is doped with metal, preferably silver (Ag).Application of an electric field with a first polarity causes aconductive pathway to grow along the sidewalls or in the sidewalls ofthe glass element, whereas an electric field of the opposite polaritydissolves the conductive pathway back into the glass element. If theconductive pathway extends between electrodes at opposite ends of theglass element, the resulting short or relatively low resistance canrepresent a logic state, e.g., a “1” state for the memory cell, whereasthe unshorted, relatively high resistance state can represent anotherlogic state, e.g., a “0” state. Additional applications for aprogrammable metallization cell include use as a variable programmableresistance and a variable programmable capacitance.

One conventional technique for producing the programmable conductormemory cell applies silver (Ag) photodoping to a chalcogenide glass suchas germanium selenide (Ge₃Se₇). The silver (Ag) photodoping processdeposits silver (Ag) over germanium selenide (Ge₃Se₇) and exposes theunderlying substrate assembly to a relatively intense source ofultraviolet (UV) radiation for an extended period of time, such as 15minutes. Disadvantageously, the photodoping process is relativelytime-consuming and can slow semiconductor fabrication rates. Thephotodoping process can decrease the overall process rate especiallywhen it is repetitively applied, such as in the fabrication of amultiple layer stack. Further disadvantageously, the extended exposureto intense UV radiation can induce the glass to convert from anamorphous material to a crystallized material, which thereby results inreduced yields.

Another disadvantage to producing memory cells with silver (Ag)photodoping of glasses is that relatively precise control of the amountof silver (Ag) that is photodiffused into the glass is necessary. Asufficient amount of silver (Ag) must be incorporated into the glassbackbone and yet, the glass must not crystallize. If too much silver(Ag) is photodiffused into the glass, the glass crystallizes. If toolittle silver (Ag) were to be photodiffused into the glass, the memorycell would not switch properly.

Another disadvantage to the photodoping process is that the ultravioletlight is attenuated by the silver film as the ultraviolet lightpenetrates through the silver film. Such attenuation variesexponentially with the thickness of the film. In one example, with 300nanometers (nm) wavelength ultraviolet radiation, the intensity of theultraviolet radiation decreases to only about 10% of its initialintensity after penetrating through 650 angstroms (Å) of silver film.This attenuation renders photodoping to be impractical with relativelythick films, and requires relatively precise control of the thicknessesof the silver (Ag) and chalcogenide glass films. In order to form athick film with a UV photodoping process, the UV photodoping process isdisadvantageously applied repetitively to relatively thin films ofsilver (Ag). In addition, the varying attenuation of the ultravioletlight continues as the silver (Ag) dopes the chalcogenide glass. Furtherdisadvantageously, this attenuation in intensity of the ultravioletlight as the ultraviolet light penetrates material results in anon-uniform depth profile of the doped silver (Ag) in the chalcogenideglass.

SUMMARY OF THE INVENTION

Embodiments of the present invention include systems and methods thatovercome the disadvantages of the prior art. The systems and methodsdescribed herein allow a chalcogenide glass, such as germanium selenide(Ge_(x)Se_(1-x)), to be doped with a metal such as silver (Ag), copper(Cu), and zinc (Zn), without utilizing an ultraviolet (UV) photodopingstep to dope the chalcogenide glass with the metal. Other examples ofchalcogenide glasses that can be used include germanium sulfide(Ge_(x)S_(1-x)) and arsenic selenide (As_(x)Se_(1-x)). Advantageously,embodiments of the invention co-sputter the metal and the chalcogenideglass and allow for relatively precise and efficient control of aconstituent ratio between the doping metal and the chalcogenide glass.Further advantageously, the systems and methods enable the doping of thechalcogenide glass with a relatively high degree of depth-profileuniformity. Also, the systems and methods allow a metal concentration tobe varied in a controlled manner along the thin film depth.

One embodiment according to the present invention is a nonvolatilememory cell including a first electrode, a second electrode, and amemory cell body disposed between the first electrode and the secondelectrode. The memory cell body includes a layer of germanium selenide(Ge_(x)Se_(1-x)) that is uniformly doped over depth with a metal such assilver (Ag), copper (Cu), or zinc (Zn).

Another embodiment according to the present invention is a depositionsystem adapted to fabricate a nonvolatile memory cell body in asubstrate assembly. The deposition system includes a deposition chamber,a first target, and a second target. The deposition chamber is adaptedto hold the substrate assembly. The deposition system is furtherconfigured to sputter metal from the first target and to sputtergermanium selenide (Ge_(x)Se_(1-x)) from the second target at the sametime to co-deposit the metal and the germanium selenide(Ge_(x)Se_(1-x)). In one arrangement, the deposition system sputterssilver (Ag) from the first target. In another arrangement, thedeposition system sputters copper (Cu) or zinc (Zn) from the firsttarget. The deposition system can further include a control configuredto control the deposition rate of the metal and the deposition rate ofthe germanium selenide such that the nonvolatile memory cell body isdeposited at a selected ratio between the metal and the germaniumselenide in the cell body.

Another embodiment according to the present invention is a process offabricating a nonvolatile memory structure in a substrate assembly. Theprocess includes forming a bottom electrode, co-sputtering metal andgermanium selenide (Ge_(x)Se_(1-x)), and forming a top electrode. Inother embodiments, a metal selenide and germanium; selenium and amixture of a metal and germanium; or a metal, germanium, and seleniumare co-sputtered.

Another embodiment according to the present invention is a process offorming a layer in a substrate assembly. The layer is capable ofsupporting the growth conductive pathways in the presence of an electricfield. The process includes providing elemental silver (Ag) in a firstsputtering target, providing germanium selenide (Ge_(x)Se_(1-x)) in asecond sputtering target, selecting a first sputtering rate for silver(Ag), selecting a second sputtering rate for germanium selenide(Ge_(x)Se_(1-x)), sputtering the silver (Ag), and sputtering thegermanium selenide (Ge_(x)Se_(1-x)) at the same time as sputtering thesilver to produce the layer.

Advantageously, the co-sputter deposition of silver (Ag) and germaniumselenide (Ge_(x)Se_(1-x)) allows the silver (Ag) to dope the sputteredgermanium selenide (Ge_(x)Se_(1-x)) in the layer with a relativelyuniform depth profile. In one arrangement, the first sputtering rate isdetermined by selecting a first sputtering power for silver (Ag), andthe second sputtering rate is determined by selecting a secondsputtering power for germanium selenide (Ge_(x)Se_(1-x)). The processpreferably further includes selecting a ratio between the silver (Ag)and the germanium selenide in the layer, using the ratio to determinethe first sputtering rate, and using the ratio to determine the secondsputtering rate.

Another embodiment according to the present invention is a process thatcontrols a constituent ratio during production of a memory cell body.The ratio is controlled by selecting a first deposition rate of a metalsuch as silver (Ag), copper (Cu), or zinc (Zn) selecting a seconddeposition rate of germanium selenide (Ge_(x)Se_(1-x)), controlling thefirst deposition rate by selecting a first sputtering power used todeposit the metal, and controlling the second deposition rate byselecting a second sputtering power used to deposit the germaniumselenide (Ge_(x)Se_(1-x)).

Another embodiment according to the present invention is a process toconfigure a deposition system used to fabricate a memory cell body for anonvolatile memory cell. The process includes receiving an indication ofa desired constituent ratio, and calculating a deposition rate for ametal and a deposition rate for germanium selenide (Ge_(x)Se_(1-x)) thatprovides the desired ratio. The calculated deposition rate for the metalis further related to a sputter power for a metal target, and thecalculated deposition rate for germanium selenide (Ge_(x)Se_(1-x)) isrelated to a sputter power for a germanium selenide (Ge_(x)Se_(1-x))target. The process configures the deposition system to sputter themetal from the metal target at the calculated sputter power, andconfigures the deposition system to sputter germanium selenide(Ge_(x)Se_(1-x)) from the germanium selenide (Ge_(x)Se_(1-x)) targetwith the calculated sputter power. The metal can be silver (Ag), copper(Cu), or zinc (Zn). In another embodiment, the process includes storinga configuration of the deposition chamber, measuring the deposition ratefor the metal versus sputter power, measuring the deposition rate forgermanium selenide (Ge_(x)Se_(1-x)) versus sputter power, and storingthe measured information such that it can be later retrieved by theprocess to configure the deposition system.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will now be described withreference to the drawings summarized below. These drawings and theassociated description are provided to illustrate preferred embodimentsof the invention and are not intended to limit the scope of theinvention.

FIG. 1 schematically illustrates a co-sputter deposition systemaccording to an embodiment of the present invention.

FIG. 2 is a schematic cross section of a memory cell with a memory cellbody formed by co-sputtering a metal and germanium selenide(Ge_(x)Se_(1-x)) glass.

FIG. 3 is a flowchart that generally illustrates a process ofco-sputtering metal and germanium selenide (Ge_(x)Se_(1-x)) glass.

FIG. 4 is a flowchart that generally illustrates a process ofconfiguring a deposition system to co-sputter metal and germaniumselenide (Ge_(x)Se_(1-x)) glass.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although this invention will be described in terms of certain preferredembodiments, other embodiments that are apparent to those of ordinaryskill in the art, including embodiments which do not provide all of thebenefits and features set forth herein, are also within the scope ofthis invention. Accordingly, the scope of the present invention isdefined only by reference to the appended claims.

Embodiments of the present invention allow a chalcogenide glass such asgermanium selenide (Ge_(x)Se_(1-x)) to be doped with a metal such assilver (Ag), copper (Cu), or zinc (Zn) without the performance of anultraviolet (UV) photodoping step. Other examples of chalcogenideglasses that can be used include germanium sulfide (Ge_(x)S_(1-x)) andarsenic selenide (As_(x)Se_(1-x)). The value of x can vary in a widerange. Although the value of x can theoretically range from 0 to 1, thefabrication of a programmable conductor random access memory (PCRAM)should maintain the value of x such that the underlying combination ofchalcogenide glass doped with the metal remains in an amorphous state.It will be understood by one of ordinary skill in the art that the valueof x can depend on the amount of the metal that dopes the chalcogenideglass. The selection of a value of x will be described later inconnection with FIG. 2.

Advantageously, embodiments of the invention co-sputter the metal andthe chalcogenide glass. This provides a relatively precise and efficientcontrol of a constituent ratio between the doping metal and thechalcogenide glass. Further advantageously, the doping of thechalcogenide glass with the metal can be produced with a relatively highdegree of depth profile uniformity. It will be understood by one ofordinary skill in the art that there are at least two types ofuniformity with respect to a doping profile. A first type, a lateraldoping profile, varies depending on the deposition system. For example,variations in the projected light intensity of an ultraviolet sourceacross the surface of the deposited film can produce lateral variationsin the doping profile. By contrast, the attenuation of the ultravioletlight as the ultraviolet light penetrates through the metal and thechalcogenide glass gives rise to variations in depth profile uniformity.

FIG. 1 schematically illustrates a co-sputter deposition system 100according to an embodiment of the present invention. The illustratedco-sputter deposition system 100 includes a first inlet 102 adapted tointroduce an inert gas, such as argon (Ar). A second inlet 104 allows avacuum pump to evacuate an interior of the co-sputter deposition system100 to a relatively low pressure.

A first target 110 provides a source of chalcogenide glass, preferablygermanium selenide (Ge_(x)Se_(1-x)). The first target 110 is coupled toa first target electrode 112, which in turn is coupled to a first powersupply 114. In one arrangement, the first power supply 114 is configuredto pulse direct current (DC) to sputter material from the first target110. In one arrangement, the first target 110 is germanium selenide(Ge_(x)Se_(1-x)), e.g., Ge₃Se₇.

A second target 120 provides the source of the metal that dopes thegermanium selenide (Ge_(x)Se_(1-x)). The metal can be silver (Ag),copper (Cu), and zinc (Zn), which will advantageously diffuse relativelyquickly into the chalcogenide element. The second target 120 is coupledto a second target electrode 122, which in turn is coupled to a secondpower supply 124. In one arrangement, the second power supply 124 isconfigured to apply direct current (DC) to sputter material from thesecond target 120.

The co-sputter deposition system 100 sputters chalcogenide glass fromthe first target 110 and simultaneously sputters the metal from thesecond target 120 to a substrate 130 to produce a layer 140 ofchalcogenide glass doped with the metal. In the illustrated co-sputterdeposition system 100, the substrate 130 rests on an electrode 106,which is at ground potential. The relative removal rates and thus,deposition rates, of material from the first target 110 and the secondtarget 120 approximately determine the doping profile of the layer 140.

FIG. 2 illustrates one embodiment according to the present invention ofa memory cell 200 with an active layer formed by co-sputtering metal anda chalcogenide glass. In one embodiment, the metal is silver (Ag). Inother embodiments, the metal is copper (Cu) or zinc (Zn). In oneembodiment, the chalcogenide glass is germanium selenide(Ge_(x)Se_(1-x)), e.g., Ge₃Se₇. The illustrated memory cell 200 includesa first electrode 202, a memory cell body 204, an insulator 208, and asecond electrode 210.

The first electrode 202 is formed on a substrate assembly. The substrateassembly can correspond to a variety of materials including plastic andsilicon. Preferably, the first electrode 202 is part of an elongatedconductor in a crosspoint array so that the memory cell 200 can beprogrammed and read. The first electrode 202 can be made from a varietyof materials and from combinations of materials such as tungsten (W),nickel (Ni), silver (Ag), and titanium (Ti).

The memory cell body 204 is formed on the first electrode 202. In theillustrated embodiment, the memory cell body 204 is a co-sputtered layerof silver (Ag) and germanium selenide (Ge_(x)Se_(1-x)). In anotherembodiment, the memory cell body 203 is a co-sputtered layer of copper(Cu) and germanium selenide (Ge_(x)Se_(1-x)) or a co-sputtered layer ofzinc (Zn) and germanium selenide (Ge_(x)Se_(1-x)). A variety ofcombinations of metal and chalcogenide glass elements can be used toform the memory cell body 204. In another embodiment, the metal andchalcogenide glass elements are co-sputtered from three separatetargets, e.g., a silver target, a germanium target, and a seleniumtarget.

The memory cell body 204 of the memory cell 200 should be formed suchthat the metal-doped chalcogenide glass in the memory cell body 204 isin an amorphous state. The skilled practitioner will appreciate thatwhere the chalcogenide glass is germanium selenide (Ge_(x)Se_(1-x)), thestate of the metal-doped chalcogenide glass, i.e., whether it isamorphous or crystalline, depends on both the value of x and the amountof metal that dopes the chalcogenide glass.

A phase diagram can be used to select a value for x and to select theamount of metal that is to dope the chalcogenide glass such that thechalcogenide glass remains amorphous. Such a phase diagram can be foundin a reference from Mitkova, et al., entitled “Dual Chemical Role of Agas an Additive in Chalcogenide Glasses,” Physical Review Letters, Vol.86, no. 19, (Nov. 8, 1999), pp. 3848-3851, (“Mitkova”) which is attachedhereto as Appendix 1 and which is hereby incorporated herein byreference in its entirety. FIG. 1 of Mitkova illustrates twoglass-forming or amorphous regions for germanium selenide(Ge_(x)Se_(1-x)) doped with silver (Ag). In one example, where x is 30,i.e., 0.30, so that the germanium selenide glass is Ge₃₀Se₇₀, the amountof silver (Ag) used to dope the germanium selenide should fall withinabout 0 to 18% or within about 23% to 32% by atomic percentage versusthe amount of selenide (Se).

In the illustrated embodiment, the insulator 208 surrounds the memorycell body 204. The insulator 208 insulates the memory cell body 204 fromother memory cells and also prevents the undesired diffusion of metalatoms and ions. The insulator 208 can be formed from a variety ofmaterials such as silicon nitride (Si₃N₄).

The second electrode 210 is formed on the memory cell body 204 and onthe insulator 208. In one embodiment, the second electrode 210 alsoforms part of a line, preferably perpendicular to a lower line as partof a crosspoint array. The second electrode 210 can be formed from avariety of materials such as copper (Cu), zinc (Zn), silver (Ag), andthe like. An electric potential applied between the first electrode 202and the second electrode 210 generates an electric field in the memorycell body 204, which in turn causes conductive pathways in the memorycell body 204 to grow or shrink in response to the applied electricfield.

FIG. 3 illustrates a process 300 of co-sputtering metal and germaniumselenide (Ge_(x)Se_(1-x)) glass. The process provides 310 a metal targetfrom which metal is to sputtered onto a substrate assembly. The metalcan be silver (Ag), copper (Cu), or zinc (Zn). The process proceeds toprovide 320 a germanium selenide (Ge_(x)Se_(1-x)) target from whichgermanium selenide (Ge_(x)Se_(1-x)) is to sputtered onto the substrateassembly. In one embodiment, the germanium selenide (Ge_(x)Se_(1-x))target is a germanium selenide (Ge₃₀Se₇₀) target.

The process proceeds to select 330 a deposition rate for the metal. Inone embodiment, the process selects a relatively constant depositionrate for the metal. In another embodiment, the process selects avariable deposition rate for the metal that can be used to vary a dopingprofile of the metal in the resulting metal-doped germanium selenide(Ge_(x)Se_(1-x)) layer. The deposition rate for the metal isapproximately related to the removal rate of material from the metaltarget. In turn, the removal rate of the material from the metal targetis approximately related to the sputter power applied to the metaltarget. This allows sputter power to control the deposition rate for themetal. It will be understood by one of ordinary skill in the art,however, that the deposition rate versus sputter power varies accordingto the configuration of the deposition system and the material that issputtered.

The process selects 340 a deposition rate for germanium selenide(Ge_(x)Se_(1-x)). In one embodiment, the deposition rate for germaniumselenide (Ge_(x)Se_(1-x)) is relatively constant. In another embodiment,the deposition rate for germanium selenide (Ge_(x)Se_(1-x)) can vary andcan be used to vary the doping profile of the metal in the metal-dopedgermanium selenide (Ge_(x)Se_(1-x)) layer. The deposition rate for thegermanium selenide (Ge_(x)Se_(1-x)) is approximately related to theremoval rate of material from the germanium selenide (Ge_(x)Se_(1-x))target and, in turn, approximately related to the sputter power appliedto the germanium selenide (Ge_(x)Se_(1-x)) target. This allows theprocess to select 340 the deposition rate by a selection of sputterpower.

The relative deposition rates between the metal and the germaniumselenide (Ge_(x)Se_(1-x)) determine the amount of doping of the metal tothe germanium selenide. For example, where a silver (Ag) deposition rateis about 17.8% of the total film deposition, the resulting film is dopedat about 32 atomic percent of silver (Ag). In another example, where thesilver (Ag) deposition rate is about 9% to about 56% of the total filmdeposition, the resulting film is doped at about 18.3% to about 69.6%silver (Ag) by atomic percentage.

The process sputters 350 the metal and the germanium selenide(Ge_(x)Se_(1-x)) from their respective targets. In one embodiment, theprocess sputters 350 metal in accordance with a direct current (DC)sputter process, and the process sputters 350 germanium selenide(Ge_(x)Se_(1-x)) in accordance with a pulse DC sputter process. In apulse DC sputter process, a positive voltage is periodically applied fora short period of time to the target to reduce or eliminate charge buildup in the target. It will be understood by one of ordinary skill in theart that the sputter power used to generate a particular deposition ratewill vary depending on the configuration of the deposition system. Forthe purposes of illustration only, one embodiment of the invention uses30 Watts (W) of DC sputter to sputter silver (Ag) and sputters germaniumselenide (Ge₃₀Se₇₀) with 575 W of pulse DC sputter to produce a dopedfilm with about 32% silver (Ag) by atomic weight.

FIG. 4 illustrates a process 400 of configuring a deposition system toco-sputter metal and germanium selenide (Ge_(x)Se_(1-x)) glass. In oneembodiment, the metal is silver (Ag), copper (Cu), or zinc (Zn) and thegermanium selenide (Ge_(x)Se_(1-x)) is germanium selenide (Ge₃₀Se₇₀). Itwill be understood that in other embodiments, a different chalcogenideglass substitutes for the germanium selenide (Ge_(x)Se_(1-x)) glass. Forexample, germanium sulfide (Ge_(x)Se_(1-x)) or arsenic selenide(As_(x)Se_(1-x)) can also be used. The process selects 410 a desiredratio for the metal to the germanium selenide in the active layer. Theratio can be relatively constant to form a relatively uniformly dopedlayer of metal-doped chalcogenide glass, or can be variable to allow ametal to dope the chalcogenide glass with a selected doping profile.

The process proceeds to calculate 420 a deposition rate for the metaland a deposition rate for the germanium selenide to produce the desireddoping of the metal in the germanium selenide (Ge_(x)Se_(1-x)). A broadvariety of methods can be used to calculate 420 the deposition rates. Inone embodiment, the process calculates 420 the deposition rates by, forexample, referring to a lookup table containing pre-calculateddeposition rates for particular doping levels. In another embodiment,the process calculates 420 the deposition rates in real time, and scalescalculations as necessary to maintain deposition rates within thecapabilities of the applicable deposition system.

The process proceeds to relate 430 the specified deposition rates tosputter power levels. Where the deposition rates of the variousmaterials sputtered versus sputter power for the configuration of thedeposition system is available, the process can retrieve the sputterpower to be used by reference to, for example, a database. The sputterpower levels for a given configuration are related to the depositionrates and can be used to control the doping profile of the depositedfilm. In one embodiment, the process collects and maintains in adatabase, the configuration of the deposition system and data ofdeposition rates versus sputter power for a collection of materialsdeposited for later retrieval.

The process proceeds to configure 440 a sputtering tool forco-sputtering. In one embodiment, the process configures the tool for DCsputter of the metal target at the specified power level for the desireddeposition rate. In one embodiment, the process configures the tool forpulsed DC sputtering of the germanium selenide (Ge_(x)Se_(1-x)) targetat the specified power level for the desired deposition rate.

While illustrated primarily in the context of co-sputtering a metal andgermanium selenide (Ge_(x)Se_(1-x)) to produce a ternary mixture of ametal-doped chalcogenide glass, it will be understood that theco-sputtering techniques described herein to fabricate a memory cellbody are applicable to other combinations suitable for formingmetal-doped chalcogenide glass elements.

One combination includes co-sputtering the metal, germanium (Ge), andselenium (Se) from three separate targets. The metal can correspond to ametal that diffuses relatively quickly into the glass, for example,silver (Ag), copper (Cu), and zinc (Zn). Another combination includesco-sputtering a metal selenide, such as Ag_(y1)Se_(1-y1),Cu_(y2)Se_(1-y2), or Zn_(y3)Se_(1-y3) with germanium (Ge) from twoseparate targets. Another combination includes co-sputtering a germaniummetal mixture, such as Ge_(z1)Ag_(1-z1), Cu_(z2)Ge_(1-z2), orZn_(z3)Ge_(1-z3), and selenium (Se) from two separate targets. In theillustrated equations, the values of y1, y2, y3, z1, z2, and z3 shouldbe maintained such that the deposited material is in an amorphous state.Advantageously, these other combinations can provide the metal-doping ofa chalcogenide glass with a relatively high degree of depth-profileuniformity and control.

The chalcogenide glass can also include germanium sulfide(Ge_(x)S_(1-x)) or arsenic selenide (As_(x)Se_(1-x)). Metal-dopedgermanium sulfide can be formed by co-sputtering metal and germaniumsulfide from two separate targets. Another combination includessputtering a metal sulfide and germanium from two separate targets.Metal-doped arsenic selenide can likewise be formed by co-sputteringmetal and arsenic selenide from two separate targets. In anothercombination, a metal arsenide and selenium are sputtered from twoseparate targets.

Various embodiments of the present invention have been described above.Although this invention has been described with reference to thesespecific embodiments, the descriptions are intended to be illustrativeof the invention and are not intended to be limiting. Variousmodifications and applications may occur to those skilled in the artwithout departing from the true spirit and scope of the invention asdefined in the appended claims.

1. A method of forming a metal-doped chalcogenide layer of a memory cellbody, the method comprising: selecting a first deposition rate for afirst material; selecting a second deposition rate of a second material;controlling the first deposition rate by selecting at least one firstsputtering power to deposit the first material; and controlling thesecond deposition rate by selecting at least one second sputtering powerto deposit the second material, wherein the first material and thesecond material are sputtered simultaneously to form a layer having apredetermined ratio of said first and second materials, wherein thefirst deposition rate and the second deposition rate are constant sothat the ratio of the deposited first material and the deposited secondmaterial is uniform over a depth of the second material.
 2. The methodof claim 1, wherein the first material is selected from the groupconsisting of silver, silver selenide, a mixture of silver andgermanium, copper, copper selenide, a mixture of copper and germanium,zinc, zinc selenide, and a mixture of zinc and germanium, and the secondmaterial is selected form the group consisting of germanium selenide,germanium and selenium.
 3. The method of claim 1, wherein a ratio of thedeposited first material and the deposited second material is selectedsuch that the deposited first material and deposited second material isin an amorphous state.
 4. The method of claim 1, further comprising:selecting a third deposition rate for a third material selected from thegroup consisting of germanium selenide, germanium, and selenium; andcontrolling the third deposition rate by selecting at least one thirdsputter power to deposit the third material.
 5. A method of forming ametal-doped chalcogenide layer of a memory cell body, the methodcomprising: selecting a first deposition rate for a first material;selecting a second deposition rate of a second material; controlling thefirst deposition rate by selecting at least one first sputtering powerto deposit the first material; and controlling the second depositionrate by selecting at least one second sputtering power to deposit thesecond material, wherein the first material and the second material aresputtered simultaneously to form a layer having a predetermined ratio ofsaid first and second materials, wherein the first deposition rate andthe second deposition rate are varied so that the ratio of the depositedfirst material and the deposited second material is varied according toa doping profile over a depth of the second material.
 6. A method offorming a metal-doped chalcogenide layer of a memory cell body, themethod comprising: selecting a first deposition rate for a firstmaterial; selecting a second deposition rate of a second material;controlling the first deposition rate by selecting at least one firstsputtering power to deposit the first material; controlling the seconddeposition rate by selecting at least one second sputtering power usedto deposit the second material, wherein the first material and thesecond material are sputtered simultaneously; and controlling at leastone of the first deposition rate and the second deposition rate so thatthe ratio between at least the first material and the second material isselectively kept uniform or controllably varied over a depth of themetal-doped chalcogenide layer.
 7. The method of claim 6, wherein aratio of the deposited first material and second material is selectedsuch that the deposited second material as doped by the first materialis in an amorphous state.
 8. The method of claim 6, wherein the firstmaterial is selected from the group consisting of silver, silverselenide, a mixture of silver and germanium, copper, copper selenide, amixture of copper and germanium, zinc, zinc selenide, and a mixture ofzinc and germanium.
 9. The method of claim 6, wherein the secondmaterial is selected from the group consisting of germanium selenide,germanium, and selenium.
 10. The method of claim 6, further comprising:selecting a third deposition rate for a third material selected from thegroup consisting of germanium selenide, germanium, and selenium; andcontrolling the third deposition rate by selecting at least one thirdsputter power to deposit the third material.